1. Field of the Invention
Embodiments of the invention generally relate to a load cup for transferring substrates in a chemical mechanical polishing system.
2. Background of the Related Art
Chemical mechanical polishing generally removes material from a semiconductor substrate through a chemical or a combined chemical and mechanical process. In a typical chemical mechanical polishing system, a wafer is held by a polishing head in a feature side down orientation above a polishing surface. The polishing head is lowered to place the substrate in contact with the polishing surface. The substrate and polishing surface are removed relative to one another in a predefined polishing motion. A polishing fluid is typically provided on the polishing surface to drive the chemical portion of the polishing activity. Some polishing fluids may include abrasives to mechanically assist in the removal of material from the substrate.
A wafer transfer mechanism, commonly referred to as a load cup, is utilized to transfer the substrate into the polishing head in a feature side down orientation. As the feature side of the substrate faces the load cup while the substrate is retained therein, care must be taken to avoid damage to the feature side of the substrate through contact with the load cup. For example, the feature side of the substrate may be scratched by surfaces of the load cup that supports the substrate or moves the substrate during the transfer process with the polishing head. Additionally, particulates generated during the substrate transfer or generated by contact of the substrate to the load cup may be carried on the substrate's surface to the polishing surface. During polishing, these particulates may cause substrate scratching, which results in non-uniform polishing and device defects. Therefore, it would be advantageous to minimize substrate to load cup contact.
Particulate and substrate damage may also result from misalignment between the load cup and the polishing head. Typically, the load cup and the polishing head are positioned relative to each other with close tolerances to ensure trouble-free operation. However, over the course of multiple substrate transfers, the polishing head and load cup may become misaligned relative to one another, resulting in undesirable substrate contact with the load cup and/or the polishing head. Moreover, as some polishing systems include multiple polishing heads that are loaded by a single load cup, maintaining the positional tolerances of all of the polishing heads relative to a single load cup is difficult, and the potential for load cup to polishing head misalignment and subsequent substrate damage is great.
Therefore, there is a need for a load cup that minimizes substrate damage and/or contamination during the transfer of a substrate with a polishing head.